Many consumer electronics have long been troubled by acoustic echo. In an occasion where loudspeakers and microphones coexist, microphones would receive voices of near-end speakers, background noise, and acoustic echo generated by reflecting the sounds emitted by loudspeaker. All the abovementioned sounds are transmitted to a far-end communicator via a satellite. Thus, the far-end communicator would hear the sounds he has emitted before. Such a phenomenon will impair the ability of users to recognize voices.
The abovementioned problem is normally solved with an AEC (Acoustic Echo Cancellation) system. In “IEEE Signal Processing Magazine, Vol. 16, pp. 42-69 (1999)”, C. Breining, P. Dreiscitel, E. Hansler, A. Mader, B. Nitsch, H. Puder, T. Schertler, G. Schmidt, and J. Tilp published a paper “Acoustic Echo Control. An Application of Very-High-Order Adaptive Filters”, wherein an adaptive signal processing method is used to cancel acoustic echo and improve voice quality.
However, the adaptive algorithm used by the abovementioned ABC system is very complicated. Besides, the abovementioned AEC system only uses a single microphone to acquire signals. Thus, the echo cancellation effect thereof is limited.
In order to further improve the voice quality of communication, some in the field proposed an “AEJ with AEC (Array Echo Jammer with Acoustic Echo Canceller)” system. For example, Kazunori Kobayashi and Yoichi Haneda proposed “A Hands-Free Unit with Noise Reduction by Using Adaptive Beamformer” in IEEE Transactions on Consumer Electronics, Vol. 54, No. 1, pp. 116-122, February 2008, wherein sound signals are processed by a microphone array and then by an AEC system to achieve an effect of spatial filtering, whereby is inhibited or attenuated the echo transmitted via echo paths.
The following three systematic error factors would influence the performance and robustness of the microphone array technology: (i) the magnitude and phase response error among individual microphones; (ii) the position error between the intended location and the real acoustic center of the microphone; (iii) the pointing error caused by the signals transmitting via the paths deviating from the principal axis of the microphone array. With size reduction of microphones, the influence of the abovementioned factors grows stronger. Therefore, the microphone array-based echo cancellation technology still has room to improve.